Microplastics inhalation and their effects on human health: a systematic review

Abstract Background Microplastics (MPs) are defined as small particles less than 5 mm in size occuring in the environment as a consequence of plastic pollution. MPs are classified into primary MPs, which are created for industrial uses, and secondary MPs, that derive from the degradation of larger plastic items. With the global increase in plastic production, MPs have become widely distributed in the natural ecosystems and have been charged with causing several detrimental effects on both the environment and on human health. Moreover, plastics often include additives to improve their properties, which may produce additional toxic substances. Humans can be exposed to MPs through different pathways, including ingestion, inhalation and dermal contact. The aim of this systematic review is to synthesize whether inhaled microplastics and plastic additives have negative effects on human health. Methods MEDLINE, Scopus and Web of Science were searched starting from December 2021. The systematic review was conducted according to the PRISMA guidelines. Eligible studies were primary studies which reported the effects of inhaled MPs on the respiratory system. Appropriate quality assessment tools were used according to the study design of primary studies. Results 38 studies met the inclusion criteria. Most of the studies were conducted in vitro, while there was a scarcity of papers that investigated the effects of MPs in population cohorts. Preliminary results show that MPs can induce pro-inflammatory or pro-carcinogenic effects by different mechanisms, depending on particles’ concentration, size, type and surface charge. Conclusions Literature has underlined several negative health concerns resulting from the absorption of microplastics and plastic additives. By gathering this information, this systematic review sheds light on the possible threats of MPs inhalation to human health and discusses whether an implementation of new public health policies for the foreseeable future is needed. Key messages • Inhalation is a major route of exposure to microplastics. • Inhaled microplastics or plastic additives may have detrimental effects on human health, promoting respiratory diseases or carcinogenic processes.


Background:
Microplastics (MPs) are defined as small particles less than 5 mm in size occuring in the environment as a consequence of plastic pollution. MPs are classified into primary MPs, which are created for industrial uses, and secondary MPs, that derive from the degradation of larger plastic items. With the global increase in plastic production, MPs have become widely distributed in the natural ecosystems and have been charged with causing several detrimental effects on both the environment and on human health. Moreover, plastics often include additives to improve their properties, which may produce additional toxic substances. Humans can be exposed to MPs through different pathways, including ingestion, inhalation and dermal contact. The aim of this systematic review is to synthesize whether inhaled microplastics and plastic additives have negative effects on human health. Methods: MEDLINE, Scopus and Web of Science were searched starting from December 2021. The systematic review was conducted according to the PRISMA guidelines. Eligible studies were primary studies which reported the effects of inhaled MPs on the respiratory system. Appropriate quality assessment tools were used according to the study design of primary studies. Results: 38 studies met the inclusion criteria. Most of the studies were conducted in vitro, while there was a scarcity of papers that investigated the effects of MPs in population cohorts. Preliminary results show that MPs can induce pro-inflammatory or procarcinogenic effects by different mechanisms, depending on particles' concentration, size, type and surface charge.

Conclusions:
Literature has underlined several negative health concerns resulting from the absorption of microplastics and plastic additives. By gathering this information, this systematic review sheds light on the possible threats of MPs inhalation to human health and discusses whether an implementation of new public health policies for the foreseeable future is needed.

Key messages:
Inhalation is a major route of exposure to microplastics. Inhaled microplastics or plastic additives may have detrimental effects on human health, promoting respiratory diseases or carcinogenic processes.

Issue:
Urbanization is a cause of climate change, as cities are where these changes are most visible. Climate change also leads to significant inequalities and health issues in urban settings. In this context, urban health promotion is mandatory to increase adaptive capacity. Since the late 1980s the World Health Organization (WHO) has emphasized schools' role in promoting health, as they can play a crucial role in increasing health awareness to future urban inhabitants.

Description:
The objective of this pre/post-interventional study is to measure the awareness of urban health and green spaces among high school students and to rise it through an educational intervention. Four interactive sessions were delivered to 319 students from 13 to 18 years old in a high school in Rome, Italy during spring 2022. Data was gathered anonymously and analysed using descriptive and inferential statistics.

Results:
A total of 192 (60%) students successfully completed the pre/ post-intervention surveys. An increase in students' knowledge of urban health and urban green areas was observed. Before the intervention 11.8% of participants were aware of urban health, whereas after the intervention 87.5% were aware. A rise across different areas appeared to be related to how many times the teachers repeated that concept during the intervention. For topics discussed in more than one session, the increase in correct answers averaged 13.9%. Two different trends emerged from the data analysis: one whose post-intervention test improved on most of questions and one whose postintervention test remained unchanged.

Lessons:
The results of the present study suggest that school-based interventions using interactive approaches on climate change and urban health are effective for increasing the knowledge level of scholars on these topics, and can be a useful way to promote health in an urban setting. This type of approach maintains high levels of concentration and interest in most students.
Key messages: Urban health training activities in schools are needed to empower youth who live in urban settings. Interactive sessions keep student concentration high and improve their participation.